Small interfering ribonucleic acids (siRNA) are a type of double-strand RNA molecules composed of more than 20 nucleotides, which can exert an effect of silencing gene expression by specifically degrading the messenger ribonucleic acids (messenger RNA, mRNA) of target genes, and this process is called RNA interference (RNAi) and plays an important role in gene regulation and growth and development, etc. RNA interference (RNAi) is an antiviral mechanism. It is a sequence-specific posttranscriptional gene silencing of homologous genes mediated by dsRNA, and the effective mode of action thereof in cells is siRNA. RNA interference can utilize a siRNA or siRNA expression vector to specifically silence target genes, and this mode is rapid, cost-effective, simple and convenient, and has high sequence specificity, which can knock out the expression of target genes in a manner of acquiring loss of function or reducing the specificity of mutant sequence, and become an important research means for discovering gene functions. Progresses have been made in antiviral and tumor studies since RNAi can specifically down-regulate the expression and replication of particular genes. During the research on gene therapy with respect to HIV-1, hepatitis B, hepatitis C and the like using RNA interference technology, it has been discovered that selecting a sequence from a viral genome without homology to human genome as an inhibitory sequence can inhibit the viral replication while avoiding the toxic and adverse effects on normal tissues. Meanwhile, the inhibitory sequence which is selectively located at the particular site can produce apoptosis-inducing effects on partial malignant tumor cells which have definite gene mutation. In addition, siRNA expression directed to certain oncogenes or apoptosis molecules can yet be induced through using tumor-specific promoters, thereby achieving the purpose of specifically killing tumor cells.
Small interfering ribonucleic acids (siRNA) which can play a role in more specifically inhibiting target genes through artificial design of a siRNA sequence are widely used in gene regulation. Although RNA interference has been widely used in various aspects in biomedicine research, there are currently still some problems for this technology which are difficult to solve. Among them, the poor stability and low efficiency in delivering siRNA are the main reasons which hamper its application. Research have shown that the artificially synthesized siRNA which belongs to the small RNA family is generally rather unstable and liable to be degraded by the RNase in the circulatory system and becomes more intolerant to the acidic and basic environment in the digestive tract. For example, RNase belonging to the RNase A family in serum leads to the degradation of siRNAs (Haupenthal et al., Inhibition of RNase A family enzymes prevents degradation and loss of silencing activity of siRNAs in serum), therefore, the inhibition of RNase A in serum can prevent the weakness of degrading and silencing effects of siRNAs. The study also indicated that the degradation of siRNA is closely related to its sequence. Therefore, a variety of measures (including chemical modification, liposome encapsulation and the like) would be tried when applying siRNA in order to resist the degradation by the RNase.
Micro-ribonucleic acids (microRNA) are defined as a kind of evolutionarily conserved non-coding single-strand small ribonucleic acid molecules of approximately from 19 to 23 nucleotides in length. MicroRNA is capable of being completely paired with target mRNA, mediating the degradation of target mRNA or inhibiting the translation of proteins encoded by target mRNA, and regulating the gene expression at a posttranscriptional level as a regulator of gene expression. MicroRNA exists extensively within the genomes of animals and plants. Recent research finds that microRNA plays a very important role in the temporal regulation and the occurrence of diseases in organisms. MicroRNA is capable of controlling the growth, differentiation, and apoptosis of cells, and participating in many normal physiological activities, such as the individual development, tissue differentiation, apoptosis, and energy metabolism and the like in organisms; meanwhile, the expression of microRNA is related to cancers and plays an important role in the course of tumor formation. Approximately half of the upstream genes of microRNA are located at the tumor-related areas within chromosomes, which can play the role of oncogene and also can play the role of tumor suppressor gene during the occurrence and development of tumors. Plant microRNA likewise has no open reading frame (ORF) as animal microRNA and manifests evolutionary conservation and has higher complementarity with its target gene sequences. The binding sites of plant microRNA and target genes are not only limited to the 3′ untranslated region (untranslated region, UTR) of the target genes, but also located at the transcribed region. Plant microRNAs are a kind of negative regulators for the gene expression of eukaryotes, which regulate the expression of plant gene mainly at a posttranscriptional level through medicating the cleavage of mRNA target molecules or reducing the translation of the target molecules, thereby regulating the morphogenesis of plant organs, growth and development, hormone secretion, and signal transduction, and the ability of response of the plants to the stress factors of the external environment.
Although microRNA has been widely used in biomedicine research, currently there exists some problems which are the main reasons that hamper its further development, for example, how to effectively deliver microRNA into animal body and allow it to function adequately in vivo. The effective contents of some microRNAs which have important functions on human and animals are relatively low in animals and plants, and it is very hard to reach a therapeutically effective amount per food intake by means of direct food intake.
Currently, the carriers for siRNA or microRNA are primarily liposomes, millimicrocapsules (Nanocapsules/Nanoparticles), -β cyclodextrin clathrate compound (β-cyclodextrin inclusion Compound) or β cyclodextrin capsules and the like; although the efficiency of delivering siRNA or microRNA is improved to some extent, the stability and efficiency are insufficient, and there is considerable toxicity.
Therefore, there is an urgent need for a more stable, efficient, and safe carrier for siRNA and/or microRNA and a method for delivering siRNA and/or microRNA.